Bt corn flap

[Chris J. Durden]

At 07:52  29/03/00 GMT, you wrote:
>On Wed, 29 Mar 00 14:14:10 GMT, Neil at nwjones.demon.co.uk (Neil Jones)
>wrote:
>
>>
>>The so called Toxin expressed in the BT corn is NOT identical to that
>>produced in organic control agents. 
>
>Well, it's the delta-endotoxin gene from Bt var kurstaki, which is the
>strain used for lepidoptera control. How about this : The toxin (and
>it is a toxin, see later) expressed in Bt corn is identical to the
>major component of the toxin produced in one of the commonest organic
>control agents.
>
>>Bacillus thurigiensis is a specialised
>>bacerial predator of invertebrates.
>
>We don't know too much about the 'normal' ecological niche for Bt but
>it seems to be a bacterium that lives as a conventional saprophyte a
>lot of the time and only occasionally kills insects. It's certainly
>not an obligate specialised predator.
- - - -- - -
  I have been seeing one form of either *B. thuringensis* or polyhedrosis
viris with some frequency since 1954. It occurs on butterfly larvae that
feed on nettles *Urtica* spp. It wipes out a population in about 3 days,
leaving the larvae as black limp sacks hanging from the claws of a proleg.
I see it most often in remote wilderness areas. Species that I have seen
affected are *Vanessa atalanta*, *Nymphalis milberti* and *Polygonia
satyrus*. It seems to be a very real fact of life/death for these species
and may prevent them from eradicating the hostplants, which are not common
in boreal regions.
- - - - -(Chris)
>
> It exists is a variety of strains which
>>differ from each other. These natural predators are one of the factors which
>>influence the population dynamics of many species. For example Bacillus
>>species are a major natural cause of mortality in the endangered Jamaican
>>Swallowtail Papilio homerus.
>>
>
>Intersting. Do you have a reference for the P. homerus stuff? I'd like
>to know more. Most of the reports I'm aware of of Bt causing much
>mortality in wild populations comes from stored product pests, which
>live in environments that are particularly good for Bt spores and
>toxin to survive in (dry, no UV), and it doesn't seem to be important
>in the population dynamics of many species in natural environments.
>
>>Engineered corn contains PART of a gene from ONE strain of Bacillus
>>thurigiensis. This is an important factor to take into consideration.
>>
>>The variability of wild Bacillus thurigiensis is an important tool in its
>>armoury. The "toxin" (actually a tool for enabling it to gain access to
>>the insect's body) exists in nature in such a range of forms that it is
>>difficult for insects to develop immunity.
>
>You seem to have some resistance with calling it a 'toxin'. Consider
>the following
>
>1) When an insect ingests Bt toxin, the toxin binds to the gut wall if
>the insect is of a species susceptible to that strain of Bt. It
>creates large pores in the cell membranes, disrupting their water
>balance and causing them to rupture. The gut lining of an insect
>that's ingested Bt toxin looks like someone's fired a shotgun at it if
>you look at it with an SEM.
>
>2) Some species of insect are killed just by the action of the toxin
>(i.e. Bombyx mori, Plodia interpunctella). Many others are killed by a
>combination of the toxin action and septicaemia from the bacterium.
>
>3) If it isn't a toxin, then why are plants expressing the gene
>protected from insect pests?
>
>Sounds like a toxin to me...
>
>>However the ecological consequences of flooding an ecosystem with high
>>levels of one specific form of the toxin are difficult to predict.
>
>Well not really. What will happen is:
>
>>...  resistance will rapidly spread in the
>>populations of many species. It is also likely that this will facilitate
>>the developement of resistance to other wild strains. This could easily
>>occur once the majority of the population of a species carries a gene
>>that that works against one strain. Natural selection works just
>>like this.
>>The consequences are that we actually decrease the ability of Natural
>>predators to control pests. That is not a smart thing to do.
>
>Quite right. Unfortunately as far as I'm aware the organic industry
>doesn't seem to be doing a great deal to manage the resistance that
>may develop from their use of 'high levels of one specific form of the
>toxin', which many of them are doing, I'm afraid.
>
>>
>>What also worries me is that the industry has chosen repeatedly to
>>describe Bacillus thurigiensis as a "soil bacterium" this is
>>not truthful at all. I tend to distrust people who are not truthful.
>>
>
>Well Neil, the thing is that Bt IS a soil bacterium. If you want to
>find Bt, look in the soil. Most isolates of Bt come from the soil.
>It's a damn sight easier to find it in the soil than it is in diseased
>insects, for example.
- - - - -
Is it growing in the soil, or merely biding its time? A lot of biota that
cannot be described as soil biota, occurs there when waiting for
opportunities elsewhere.
- - - - -(Chris)
 It is also found elsewhere, I'll grant you that,
>but if you want to describe Bt and you only have two words, 'soil
>bacterium' is pretty good. 
>
>I would be interested to know your source for this information: maybe
>someone in the organic food industry is not being truthful. Remember,
>it is an industry, and whereas some organic growers are dedicated
>selfless protectors of the environment there are others who are in it
>for the money, and they stand to lose big wads of cash if the public
>decides that one of their most effective control agents is no longer
>acceptable.
- - - -
Wow. You could say that about the GM/GE nebbishes too!
- - - -(Chris)
>
>Best wishes
>
>Rob Knell
>
>